1. Field of the Invention
The present invention relates to a method for controlling the operation of a variable displacement refrigerant compressor, especially a variable displacement wobble plate type compressor accommodated in a car-conditioner and driven by a car engine via a solenoid clutch. More particularly, it relates to a method for controlling the operation of a variable displacement wobble plate type compressor accommodated in a car air-conditioner by which an acceleration of a car engine is not adversely affected when starting the car after stopping or parking the car for a long period of time.
2. Description of the Related Art
Generally, a variable displacement refrigerant compressor accommodated in a car air-conditioner is driven by a car engine via a solenoid clutch, and therefore, when the car is to be started or accelerated, a large load due to inertia of the car per se, and an additional load due to the inertia of the variable displacement refrigerant compressor of a car air-conditioner, are simultaneously applied to a car engine, and accordingly, the acceleration of the car engine is adversely affected.
Japanese Unexamined Patent Publication No. 56-112314 discloses a measure for solving such problems of the conventional car air-conditioner. Namely, a device is employed to monitor a negative pressure level in a car engine, and when the device detects that the negative pressure level of the car engine has dropped much lower than a predetermined level, due to an acceleration of the car, a solenoid clutch arranged between the car engine and a variable displacement refrigerant compressor is disconnected to stop the operation of the compressor. Thus, an application of an additional load to the car engine can be prevented, and therefore, an acceleration of the car engine is not adversely affected. Nevertheless, after completion of the acceleration of the car, when the solenoid clutch is connected to drive the refrigerant compressor, the operation of the compressor is immediately started under a large displacement or capacity condition, and therefore, a large load is instantly applied to the car engine. As a result, a large corresponding torque is transmitted from the car engine to the compressor, and slippage of the solenoid clutch occurs, which shortens the life of the solenoid clutch. Also, the shock of the above-mentioned instant application of a large load to the car engine is transmitted to the car driver.
Japanese Unexamined Patent Publication No. 57-191118 discloses a proposal for a control device to solve the above problems encountered by the latter conventional car air-conditioner incorporating therein a variable displacement compressor. Namely, the control device reduces a displacement of a variable displacement refrigerant compressor to a minimum level by driving a displacement changing element of the compressor immediately the starting switch or ignition switch of the car is turned ON. But, when the control device is applied to a car air-conditioner including a wobble plate type variable displacement refrigerant compressor as disclosed in, for Example, U.S. Pat. No. 4,688,997 to Suzuki et al, and incorporating therein a non-rotary wobble plate capable of changing the angular position thereof to vary the stroke of pistons and thereby vary the compressor displacement, a problem arises in that, since the angular position of the wobble plate is controlled and determined by a dynamic relationship between a pressure prevailing within a crankcase of the compressor, a pressure prevailing in a discharge chamber of the compressor, and a force of a return spring acting to return the wobble plate to a predetermined position, it takes a long time for the wobble plate to move to the minimum displacement position from the other displacement positions. Namely, an immediate move of the wobble plate to an erect position thereof at which the piston stroke becomes smallest does not take place, and as a result, when the car engine is operated to start the car, it is in practice difficult to start the car with a good acceleration from a stop thereof.